1. Field of the Invention
The present invention relates to a wiring pattern, an electronic device, an organic semiconductor device, a layered wiring pattern, and a layered wiring substrate using the wiring pattern, and more particularly to a shape of a conductive pattern of a wiring pattern and a configuration including the wiring pattern such as an electronic device, an organic semiconductor element, a layered wiring pattern, and a layered wiring substrate.
2. Description of the Related Art
Conventionally, although photolithography methods are used for forming wirings of semiconductor devices and electronic circuits, the use of such photolithography methods requires expensive facilities. Furthermore, the long and complicated procedures of the photolithography methods lead to an increase of manufacturing cost. Recently, a method of forming a wiring pattern by coating liquid containing conductive fine particles directly onto a substrate has been drawing attention, and various proposals have been made using the method.
For example, Japanese Laid-Open Patent Application No.2003-142802 (hereinafter referred to as “Patent Document 1”) discloses a method of forming a linear pattern by coating a liquid containing pattern forming material onto a substrate in a manner where the linear pattern has at least one corner formed by at least two lines and a protruding part extending from the corner. That is, in a case where wiring is formed by coating ink onto a water-repellent substrate, problems such as disconnection may occur due to a large portion of the ink concentrating at a bent corner part of the wiring while only a small portion of the ink is provided at areas other than the corner part. However, with the Patent Document 1, ink can be prevented from concentrating at a corner since an intersection is formed at the corner by extending the wiring. Thereby, disconnection due to creation of a bulge (liquid reservoir) or short-circuiting can be prevented.
As another example, Japanese Laid-Open Patent Application No.2004-290958 (hereinafter referred to as “Patent Document 2”) discloses a method for increasing the width of a film pattern including the steps of forming a center part of a film pattern by applying liquid droplets (Step 1), forming one side part with respect to the center part (Step 2), and forming the other side part with respect to the center part (Step 3). Since the droplets applied to the center part are either dry or highly viscous at the time of conducting Steps 2 and 3, droplets will not flow and concentrate even when liquid droplets are coated onto the side parts. Thus, bulges (liquid reservoirs) which tend to be formed when increasing the width of a pattern can be prevented from being created at an in-plane area of a substrate. Thereby, disconnection and short-circuiting can be prevented.
Although the methods disclosed in Patent Documents 1 and 2 can prevent a concentration of liquid droplets from causing short-circuiting and disconnection in an in-plane direction (between linear patterns, between film patterns) of a substrate, the methods cannot prevent bulging of liquid droplets at an end part (corner part) of wiring with respect to a cross-sectional direction of the substrate (film thickness direction). Therefore, in a case where an electrode pattern is provided on the above-described linear pattern or film pattern via an insulating layer, insulation failure may occur and result in short-circuiting of wires between the layers of a substrate.
As another example, Japanese Laid-Open Patent Application No.2004-335849 (hereinafter referred to as “Patent Document 3”) discloses a method of forming a film pattern by jetting small diameter liquid droplets in a manner burying a groove part(s) of a wiring pattern. In forming a thin film pattern on a substrate with the method of Patent Document 3, liquid droplets are jetted in a manner so that droplets are not drawn together and are prevented from integrating with each other (forming of a bulge). With the film pattern formed by this method, acute areas can be prevented from being formed at the edge parts (side parts) of a wiring part. Thereby, generation of high frequency noise can be reduced.
Although the method disclosed in Patent Document 3 reduces generation of high frequency noise by burying the groove parts formed at side areas of a pattern formed by connecting liquid droplets in an in-plane direction of a substrate (as shown in FIGS. 1 and 2 of Patent Document 3), the method does not prevent bulging of liquid droplets in the cross-sectional direction (film thickness direction) of the substrate. Since this method is for forming thin film patterns while sequentially drying the droplets jetted onto a substrate so as to prevent forming of bulges, it is difficult to apply this method, which increases a wet area by integrating droplets jetted onto a predetermined thin film pattern area and then dries the wet area.
As another example, Japanese Laid-Open Patent Application No.2005-285843 (hereinafter referred to as “Patent Document 4”) discloses a method of manufacturing a thin film transistor and a display device in which the number of times for conducting a photolithography process is reduced. Patent Document 4 concerns an invention of a shape of a gate electrode. In Patent Document 4, by forming a gate electrode into a shape having a concave part, displacement of a gate insulating film and a source/drain electrode (which are formed in a subsequent process) can be reduced. Although a schematic configuration of the electrode is shown in, for example, FIGS. 1-7 and FIGS. 9-12 of Patent Document 4, neither the problem of film bulging at end parts (particularly, corner parts) of an electrode when forming electrode layers with a printing method nor countermeasures for the problem are taken into consideration in Patent Document 4. Therefore, the problem of bulging or its countermeasures are not described in Patent Document 4.
As another example, in Japanese Laid-Open Patent Application No.2005-310962 (hereinafter referred to as “Patent Document 5”), the inventor of the present invention proposes a layered configuration which can easily form fine patterns with a printing method using a variable wettability material. The critical surface tension of the variable wettability material can change in accordance with energy applied thereto. For example, FIG. 1 and FIGS. 6-10 of Patent Document 5 are schematic views of a conductive layer of the layered configuration. However, in a case of forming a conductive pattern having a corner part(s) by applying liquid droplets (conductive liquid material), the problem of bulging of the conductive film at the corner part is not taken into consideration in Patent Document 5 and is not described in Patent Document 5. Therefore, insulation failure due to bulging of the conductive film tends to occur in a case where a layered wiring configuration is obtained by forming a wiring pattern on the above-described layered configuration via an insulating layer.
That is, in a case of forming a conductive pattern (hereinafter also simply referred to as “pattern”) by applying a conductive liquid material (hereinafter also referred to as “ink”) to a variable wettability material having a critical surface tension (surface energy) that changes in accordance with energy applied thereto, ink becomes confined (trapped) in a high surface energy part (area having high surface energy) of the variable wettability material. Since the amount of ink at the vicinity of a center part of the pattern is greater than that of a peripheral area and the vapor pressure of the ink solvent of the ink contacting the atmosphere becomes higher toward the vicinity of a center part of the pattern, the evaporation rate of the ink becomes slower. That is, the amount of evaporation per unit of time becomes less. On the other hand, since the vapor pressure of the ink solvent of the ink contacting the atmosphere becomes lower toward the outer peripheral part of the pattern, the evaporation rate of the ink becomes faster. That is, the amount of evaporation per unit of time increases at the outer peripheral part of the pattern.
As shown with a plan view of FIG. 1, since ink covers only a small area at the corner parts of the pattern, the vapor pressure of the ink solvent of the ink contacting the atmosphere is particularly low at the corner parts. Therefore, the evaporation rate of the ink is extremely fast at the corner parts. In a case where ink is applied as a pattern to a high surface energy part of a variable wettability material, the difference of the evaporation rate between the corner parts of the pattern and other parts of the pattern causes ink to flow from an area having a slow evaporation rate (center part of the pattern) to an area having a fast evaporation rate (outer peripheral part (particularly, corner part) of the pattern). FIGS. 2A and 2B are for describing the flow of the ink, where FIG. 2A is a plan view of the variable wettability material and FIG. 2B is a cross-sectional view taken along line B-B of FIG. 2A. The lengths of the vertical arrows shown in FIG. 2B indicate the amount of evaporation at corresponding parts of the variable wettability material. FIG. 3 is a schematic diagram for describing the flow of ink by using isochronal lines in a case where ink is applied to a wettability area including a right-angle corner part.
FIG. 3 shows how ink evaporates at an outer peripheral part of the wettability area and flows toward an outer part (outer peripheral part) of the pattern. In FIG. 3, Part A indicates an area where the ink film thickness is large, and Part B indicates an area where the ink film thickness is particularly large. For example, in a case where time t=t4 elapses, line L4 in FIG. 3 reaches an outer peripheral part of the pattern. Accordingly, the solid content of ink located between the outer peripheral part and the line L4 begins to gather at the vicinity of the outer peripheral part and causes the film thickness of the outer peripheral part to increase. As shown in FIG. 3, since the distance between the line L4 and the outer peripheral part of the pattern at the corner part (in this example, Part B) is greater than the distance between the line L4 and the outer peripheral part of the pattern at a non-corner part (in this example, Part A), the amount of solid content gathering at the vicinity of the outer peripheral part increases. Thereby, the corner part (Part B) becomes thicker than the non-corner part (Part A). Thus, a projecting film thickness peak (convex protrusion) is formed at the corner part of the pattern. That is, a bulge is formed at the corner parts of the pattern, to thereby form a mountainous shape. It is to be noted that the bulges with large thicknesses may sometimes sink (cave in) after drying, to thereby form a concave part(s) in the film surface of the pattern.
For example, in a case where a conductive pattern including a right angle corner part is formed on a high surface energy part of a variable wettability layer, the film thickness increases at end parts and bending parts of the pattern (particularly, at corner areas of the end parts and bending parts) as illustrated with hatchings in FIG. 4. As a result, bulges are created at end parts and bending parts of the pattern (particularly, at corner areas of the end parts and bending parts). For a conductive pattern having a wide thickness distribution, the drying property and the baking property tend to significantly differ between a thick part and a thin part of the pattern. This results in inconsistent conductivity.
Furthermore, in a configuration having a conductive pattern layer formed on a high surface energy part of a variable wettability layer, that is, in a case of fabricating a layered wiring substrate by depositing a wiring pattern (conductive pattern) on an insulating film and forming an electrode layer (another conductive pattern layer) thereon, a large bulge in the thickness of the conductive pattern layer causes the insulating film to become relatively thin at the area of the bulge. That is, the space between the electrodes (conductive layers) becomes relatively narrow at the bulge and is reduced in insulation capability (see FIG. 5). Thereby, the electric field tends to concentrate at the bulging area. This leads to insulation breakdown of the insulating film and adversely affects the functions of the layered wiring substrate. FIG. 5 is a schematic diagram for describing how the electric field between electrodes tends to concentrate at the bulging area.